The new health insurance marketplaces appear to be making little headway in signing up Americans who lack insurance, the Affordable Care Act’s central goal, according to a pair of new surveys.

Only one in 10 uninsured people who qualify for private plans through the new marketplaces enrolled as of last month, one of the surveys shows. The other found that about half of uninsured adults have looked for information on the online exchanges or planned to look.

The snapshots from the surveys released Thursday provide preliminary answers to what has been one of the biggest mysteries since HealthCare.gov and separate state marketplaces opened last fall: Are they attracting their prime audience?

The findings emerge as the Obama administration has been revising a series of rules that define how the 2010 law works in practice. According to a variety of health-policy experts who support and oppose the law, the changes are in response to consumer hesitancy and political opposition that linger — at least, in the early going — as the law’s major provisions have taken effect.

The rule changes have postponed or relaxed aspects of the law, sometimes to adjust for technical problems, other times to push into the future controversies that have arisen from specific groups of consumers or parts of the health-care industry.

This week, administration officials said that people could keep for three years health plans whose benefits do not meet the law’s standards. Last week, they said the government would pay for people in certain states to collect federal subsidies for insurance policies outside the exchanges. Two weeks before that, they gave medium-size and large employers two additional years before they must offer coverage to their full-time workers.

The surveys offer no evidence that the rule changes contribute to the insurance marketplaces’ relatively low popularity among the nation’s uninsured. One of the surveys, by the consulting firm McKinsey & Co., shows that among people who are uninsured and do not intend to get a health plan through one of the exchanges, the biggest factor is that they believe they cannot afford it.

The McKinsey survey shows that of people who had signed up for coverage through the marketplaces by last month, about one-fourth described themselves as having been without insurance for most of the past year. That 27 percent, while low, compares with 11 percent a month earlier.

The survey also attempted to measure what has been another fuzzy matter: how many actually have the insurance for which they signed up. Under federal rules, coverage begins only if someone has started to pay their monthly insurance premiums. Just over half of uninsured people said they had started to pay, compared with nearly nine in 10 of those signing up on the exchanges who said they were simply switching from one health plan to another.

The second survey, by researchers at the Urban Institute and based on slightly older data from December, shows that awareness of the new marketplaces is fairly widespread but that those with a lower income and those who are uninsured are less likely to know about this avenue to health coverage than other people.

The surveys are not a perfect way of showing what is happening in the insurance exchanges. But they begin to fill in blanks that both advocates and opponents of the 2010 health-care law agree are critical to understand.

“If there is one point to the law, it is to lower the number of uninsured,” said Larry Levitt, a senior vice president at the Kaiser Family Foundation, a health-policy organization. “Ultimately, that has to happen for the law to be judged a success.”

With just over three weeks remaining in a six-month sign-up period, the question of how many uninsured people are gaining coverage is eluding both Obama administration officials and most of the private health plans being sold through the new marketplaces.

Inside the Department of Health and Human Services, staff analysts who have been producing monthly enrollment updates are confronted with a major hindrance to examining the question of people’s prior insurance status: the wording of the HealthCare.gov applications themselves.

The paper versions of applications, used by a small fraction of people who are signing up, contain a multiple-choice question asking whether people in a household currently have insurance. “No” is one of the boxes people can check.

But the online application, which most people use to enroll, asks whether people want to apply for coverage but does not give them a place to indicate whether they have insurance now or have had it in the past. As a result, HHS analysts have no way to assess how many of the online enrollees were uninsured in the past.

“We are a looking at a range of data sources to determine how many marketplace enrollees previously had coverage,” said Julie Bataille, director of the Office of Communications at the Centers for Medicare and Medicaid Services (CMS), the HHS agency overseeing the new insurance marketplaces. “Previous insurance coverage is an important metric, and we hope to have additional information in the future,” she said.

In the absence of information from people who have enrolled, Obama administration officials have drawn attention to recent outside polls that suggest that the overall number of uninsured Americans is declining. It is not clear, however, whether the trend is because of the health-care law or other reasons.

So far, of 14 states operating their own insurance exchanges, instead of relying on the federal one, only New York has given any indication about how many uninsured people are signing up.

The NY State of Health, the state’s marketplace, said last month that including people eligible for Medicaid, 70 percent of the half-million people who had enrolled since it opened in October were uninsured at sign-up time.

The McKinsey survey, the firm’s fourth since late November to measure the behavior of Americans in the new insurance marketplaces, is based on a national sample of about 2,100 people.

It defined uninsured people as those who qualify for private health plans sold through the exchanges. It does not include those who are uninsured and have an income low enough that they qualify for Medicaid. The Urban Institute’s survey includes people eligible for Medicaid in its definition of the uninsured.

McKinsey’s survey also includes people who bought insurance outside the new marketplaces. Asked at a conference on Thursday how many Americans are buying insurance on their own, apart from the new marketplaces, Gary Cohen, the outgoing director of CMS’s Center for Consumer Information and Insurance Oversight, said that federal health officials have not yet tried to collect such information. “I think it is a really important question, because obviously the goal is to get as many people insured as possible,” he said.

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